U.S. Pat. No. 3,542,273 dated Nov. 24, 1970, inventor Granville R. Hedrick, discloses a nail driving device especially used for driving nails into a wooden flooring by means of a source of compressed air. The device of this patent is alternately operated by an external impact blow accomplished on the device anvil while the operator's other hand holds a handle of the device; or by squeezing a trigger accessible to the hand holding the handle. The device in accordance with this prior patent thus has a trigger initiated operating system, which is used only as an alternative to the impact blow initiating system. One main disadvantage of the Hedrick nailer is that it does not provide any reliable security means for preventing the nails from being accidentally expelled from the nailer.
U.S. Pat. No. 4,907,730 in 1990, inventor Jean-Paul Dion, shows a pneumatic nailer which includes a feeler disc which must be applied against the ground for the nail driving operation to occur. Indeed, when the feeler disc is applied against the ground, a needle valve located inside the nailer main body closes an inner channel for allowing air to travel between chambers inside the nailer when the hammer is impacted on the anvil, and consequently for allowing the nail to be driven through the floor boards. The Dion patent however does not include a reliable security device for preventing the nails from being accidentally expelled, since the feeler disc will be activated to allow nail expulsion whenever the nailer rests or abuts on a surface with its lower surface.